Application Research On Asphalt Pavement Thickness Design Under Non-uniform Load And Dynamic Modulus Properties

Semi-rigid asphalt pavement has found its wide application in highway construction.However, due to various reasons, the service life of semi-rigid asphalt pavement is notproper. According to relevant statistics, semi-rigid asphalt pavement service life isgenerally8to10years in developed countries, while in our country, this data is usually3to5years. But there are some domestic asphalt pavements serving less than a year andthen falling into serious damage, which results not only from the construction, materialselection and overall design, but also from structural thickness design. In fact, accordingto domestic design specifications of asphalt pavement structure, because of the highstrength and small deformation of semi-rigid base, bottom layer of asphalt pavement ofsemi-rigid base is often under pressure after calculation instead of tension, causing thatthe control index of flexural stress or tensile strain design could satisfy the requirementsfor preventing the fatigue cracking in structural layer; similarly, deflection index has noeffect on layer thickness design of the structure, especially the thickness of the asphaltlayer. There are many factors causing this problem, among which, one of the mostimportant reason is that the vehicle loads and structural layer modulus with which todesign the thickness of the pavement are not accurate enough.In the commonly used mechanistic–empirical (M-E) methods for pavement structure, thewheel load is assumed to be a circular uniform load. However, even with the samevehicle load in the same pavement, the action of the wheel load is different in magnitudeand pattern, and so is the mechanical response. Meanwhile, the vehicle loading is farfrom what the uniform distribution can describe, vehicle load, tire pressure, tread patternsand other factors have a significant effect on loading distribution. The form of actualwheel load is not simply sinusoidal, but with vehicle load increasing, the waveformchanges from rectangular to half-sine. And in the case that the asphalt layer is thickenough, the waveform is almost bell-shape. In addition, according to domestic modulusspecifications, the layer structure of asphalt pavement adopts static modulus, which isobviously too simple to describe the modulus. Actually, static modulus could reflect no characteristics of the asphalt mixture. Just as AASHTO recommended, dynamic modulusshould be applied into the layer structure because the dynamic modulus can well reflectthe actual dynamic stress of asphalt pavement. But due to the fact that only the half-sinewaveform is taken into account, the dynamic modulus cannot reflect the actual stressdistribution. Therefore, based on the research achievements by AASHTO, it is necessaryto conduct further research on dynamic modulus.In this paper, two main parameters (vehicle loading and dynamic modulus) are utilized todesign thickness of the pavement structure. Firstly, the effects of the factors includingtest temperature, loading waveforms and loading frequency on the static modulus anddynamic modulus are taken into considerations, secondary development of the controlprogram of test loading on loading waveforms is made and applied to the dynamic test.Secondly, the test results are utilized to determine the static modulus and dynamicmodulus of each asphalt layer. Thirdly, by the use of ANSYS software and BISARsoftware to calculate and analyze the mechanical response of pavement structures toestablish the exact ANSYS finite element model, the finite element model of thepavement structure under different modulus combinations is established to analyze themechanical response and understand differences. Finally, the thickness of the asphaltpavement is determined under a combination of different modulus according to thecontrol index of asphalt pavement thickness designed.